dt-bindings: watchdog: ti,rti-wdt: Add support for WDIOF_CARDRESET

TI RTI (Real Time Interrupt) Watchdog doesn't support to record the
watchdog cause. Add a reserved memory to know the last reboot was caused
by the watchdog card. In the reserved memory, some specific info will be
saved to indicate whether the watchdog reset was triggered in last
boot.

Signed-off-by: Li Hua Qian <huaqian.li@siemens.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20230718021007.1338761-2-huaqian.li@siemens.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

Author: huaqianli

Documentation/devicetree/bindings/watchdog/ti,rti-wdt.yaml

@@ -34,6 +34,20 @@ properties:
   power-domains:
     maxItems: 1
 
+  memory-region:
+    maxItems: 1
+    description:
+      Contains the watchdog reserved memory. It is optional.
+      In the reserved memory, the specified values, which are
+      PON_REASON_SOF_NUM(0xBBBBCCCC), PON_REASON_MAGIC_NUM(0xDDDDDDDD),
+      and PON_REASON_EOF_NUM(0xCCCCBBBB), are pre-stored at the first
+      3 * 4 bytes to tell that last boot was caused by watchdog reset.
+      Once the PON reason is captured by driver(rti_wdt.c), the driver
+      is supposed to wipe the whole memory region. Surely, if this
+      property is set, at least 12 bytes reserved memory starting from
+      specific memory address(0xa220000) should be set. More please
+      refer to example.
+
 required:
   - compatible
   - reg
@@ -47,7 +61,18 @@ examples:
     /*
      * RTI WDT in main domain on J721e SoC. Assigned clocks are used to
      * select the source clock for the watchdog, forcing it to tick with
-     * a 32kHz clock in this case.
+     * a 32kHz clock in this case. Add a reserved memory(optional) to keep
+     * the watchdog reset cause persistent, which was be written in 12 bytes
+     * starting from 0xa2200000 by RTI Watchdog Firmware, then make it
+     * possible to get watchdog reset cause in driver.
+     *
+     * Reserved memory should be defined as follows:
+     * reserved-memory {
+     *     wdt_reset_memory_region: wdt-memory@a2200000 {
+     *         reg = <0x00 0xa2200000 0x00 0x1000>;
+     *         no-map;
+     *     };
+     * }
      */
     #include <dt-bindings/soc/ti,sci_pm_domain.h>
 
@@ -58,4 +83,5 @@ examples:
         power-domains = <&k3_pds 252 TI_SCI_PD_EXCLUSIVE>;
         assigned-clocks = <&k3_clks 252 1>;
         assigned-clock-parents = <&k3_clks 252 5>;
+        memory-region = <&wdt_reset_memory_region>;
     };